We propose to identify genes that underlie susceptibility to asthma and atopy by performing two-point and complex linkage analysis with micro-satellite markers in families with well-defined asthma. The diagnosis of asthma in all family members will be made using strict criteria based on medical history and results of spirometry and methacholine challenge studies; skin tests for inhaled antigens will be performed and total IgE, specific IgE, and eosinophil counts will be measured.